The present invention relates to inkjet printheads, and particularly, but not exclusively, to inkjet printheads having staggered fluidic ports.
In inkjet printers, it is known to provide inkjet printheads having a plurality of droplet generating units arranged adjacent each other in arrays on a substrate, each droplet generating unit having a fluidic chamber, a nozzle and an actuator associated therewith, whereby the actuators are controlled to effect ejection of droplets of fluid from the nozzles onto a print medium. Using such functionality, characters and images may be printed on the print medium in a controlled manner.
It may be desirable to increase the number of nozzles within an inkjet printhead in order to increase the resolution of the inkjet printer.
However, increasing the number of nozzles in an inkjet printhead requires increasing the number of fluidic chambers, actuators and/or the size of the substrate material and, therefore, provides engineering, fabrication, design and cost challenges.
For example, when increasing the number of fluidic chambers within a fixed sized substrate, the distance between adjacent fluidic chambers is decreased. As such, there may be less space available between adjacent fluidic chambers for routing electrical traces which may be required, for example, to provide signals (e.g. drive signals) to the corresponding actuators.
Whilst the width of the electrical traces may be decreased to take account of the reduced available space, decreasing the width of the electrical traces increases the resistance of the electrical traces, and therefore, may require larger signals to control such actuators, which may be undesirable.
Furthermore, the increased resistance may result in increased electrical current being drawn through the portions of the electrical traces having decreased width.
Furthermore still, the increased electrical current may result in increased amounts of heat being generated within the portions of the electrical traces having decreased width (e.g. localised heating), thereby leading to a failure of the electrical traces as a consequence of, for example, burnout and/or electrical fusing.
It will be appreciated that failure of one or more electrical traces may negatively impact the operational performance of the inkjet printhead. For example, if an electrical trace used to supply a drive signal to an actuator fails, then that actuator may not function correctly or not at all.
Furthermore, inkjet printheads having electrical traces comprising micrometre (μm) width dimensions may be difficult to manufacture using presently available fabrication techniques (e.g. below 4 μm may be difficult to manufacture), and, therefore, may have a poor manufacturing yield in comparison to inkjet printheads having electrical traces with comparatively wider tracks. Furthermore, such electrical traces may be prone to cracking/failure, and, therefore, may affect the reliability of the inkjet printhead.
Whilst the thickness of the electrical traces may be increased to compensate for the reduced width, increasing the thickness thereof generally requires increasing the space between the adjacent fluidic ports, which, on a substrate of a fixed size, may result in reducing the number of associated nozzles on the substrate, which, in turn, will result in a reduced resolution.
Furthermore, increasing the thickness of the electrical traces means that depositing a protecting cover layer (e.g. a passivation material) on the electrical traces may be difficult to achieve due to an increased vertical height of the sidewalls of the electrical traces.
Therefore any such protecting cover layer may be unreliable, which may lead to cracking thereof. Such cracking may, in turn, result in fluid coming into contact with the electrical traces.
Fluid contacting the electrical traces is undesirable as it may result in failure thereof, as a consequence of, for example, an electrical short circuit between the fluid and the electrical trace(s).
The thickness of the protecting cover layer may be increased in order to sufficiently cover the side walls of electrical traces having increased thickness (e.g. to reduce the likelihood of the protecting later cracking). However, increasing the thickness of the electrical traces and/or the protecting cover layer adds to the topography of the surface of the substrate on which they are deposited. It will be appreciated that increasing the topography of the surface may increase the difficulty of depositing other features/elements thereon. For example, securely bonding a capping layer to the surface of the substrate may be more challenging.